Method and apparatus for producing a metal article

ABSTRACT

A method of producing a metal article having a unidirectional grain structure in a given direction comprises the steps of heating a mould for the article to a temperature above the melting point of the metal, charging molten metal into, or melting metal in, the mould, effecting relative movement between the mould and a furnace so that said mould moves through the furnace, said furnace having a heat front which is so disposed with respect to the direction of relative movement between the mould and the furnace, so that said heat front moves substantially perpendicular to said direction towards one end of the mould, and cooling the opposite end of said mould so that said heat front produces said grain structure in the article. There is also disclosed an apparatus for carrying out the method.

United States Patent Higginbotham et al.

[ July 18, 1972 [54] METHOD AND APPARATUS FOR PRODUCING A METAL ARTICLE [72] inventors: Gordon John Spencer Higginbotham, Derby; Douglas Wilson Hall, Brailsford,

both of England [73] Assignee: Rolls-Royce Limited, Derby, Derbyshire,

England [22] Filed: July 9, 1970 21 Appl. No.: 53,514

[30] Foreign Application Priority Data July 11, 1969 Great Britain ..35,l2l/69 [52] U.S. Cl ..l64/60, 164/127, 164/338 [5 l] Int. CL. B22d 25/06 [58] Field of Search... ..164/60, 122, 125, 127, 338,

[56] References Cited UNITED STATES PATENTS 3,532,155 10/1970 Kane et al ..l64/60 Primary Examiner-J. Spencer Overholser Assistant Examiner-John E. Roethel Attorney--Cushman, Darby & Cushman [57] ABSTRACT A method of producing a metal article having a unidirectional grain structure in a given direction comprises the steps of heating a mould for the article to a temperature above the melting point of the metal, charging molten metal into, or melting metal in, the mould, effecting relative movement between the mould and. a furnace so that said mould moves through the furnace, said furnace having a heat front which is so disposed with respect to the direction of relative movement between the mould and the furnace, so that said heat from moves substantially perpendiculanto said direction towards one end of the mould, and coolingthe opposite end of said mould so that said heat front produces said grain structure in the article. There is also disclosed an apparatus for carrying out the method.

10 Claims, 2 Drawing Figures PATENIEIJ Jun 8 m2 3,577324 SHEET 1 OF 2 CH/LL i WATER WAff/Q V 007 METHOD AND APPARATUS FOR PRODUCING A METAL ARTICLE This invention relates to a method and apparatus for producing a metal article having a unidirectional grain structure parallel to a given direction, and although not so restricted, will be described with reference to the making of blades for a gas turbine engine.

According to one particular aspect of the present invention there is provided a method for producing a metal article having a unidirectional grain structure in a given direction, comprising the steps of heating a mould for the article to a temperature above the melting point of the metal, charging molten metal into, or melting metal in, the mould,.effecting relative movement between the mould and a furnace so that said mould moves through the furnace, said furnace having a heat front which is so disposed with respect to the direction of relative movement between the mould and the furnace so that said heat front moves substantially perpendicular to said direction towards one end of the mould, and cooling the opposite end of said mould so that said heat front produces said grain structure in the article.

The present invention uses a technique known as directional solidification. This technique involves arranging that the heat flow from molten metal in a mould takes place in one single predetermined direction, rather than at right angles to all faces of the mould, as in the normal casting technique. Using this directional flow of heat, it is possible to arrange that the crystals within the solidified metal are all unidirectionally disposed in a direction starting at the face at which the heat is extracted and extending linearly therefrom. As might be expected, the direction of greatest strength tends to be along the direction of the grains, while the structure is particularly resistant to cracking in a direction transverse to the grains.

The heat front, in the preferred embodiment, is disposed at an angle to the direction of movement of the article.

Said cooling may be effected by contacting said opposite end of said mould with a cooled surface. Alternatively, said cooling may be effected by directing a cooling medium upon said opposite end of the mould.

Said article may be a blade, vane or component of a gas turbine engine and said metal may be an alloy.

Said mould may be charged with molten metal while in the furnace. Alternatively, said metal may be a powder or pellets and may be placed in said mould prior to melting.

Preferably said furnace is stationary and said mould is moved therethrough.

According to another aspect of the present invention there is provided a blade for a gas turbine engine when made by the method recited in any of the preceding paragraphs.

According to a further aspect of the present invention, there is provided an apparatus for producing a metal article having a unidirectional grain structure parallel to the given direction comprising a furnace having heater means for heating a mould for the article to a temperature above the melting point of the metal, means for charging molten metal into, or for melting metal in, the mould, means for effecting relative movement between the mould and the furnace, said furnace having a heat front which is so disposed with respect to the direction of relative movement between the mould and the furnace so that said heat front moves substantially perpendicular to said direction towards one end of the mould, and means for effecting cooling of the opposite end of the said mould so that said heat front produces said grain structure in the article.

Said furnace may be linear or alternatively may be arcuate.

The means for effecting relative movement between the mould and the furnace may comprise conveyor means adapted to move a plurality of moulds through the furnace which is stationary.

A plurality of furnaces may be disposed adjacent to each other, said conveyor means being common to said plurality of furnaces.

Said cooling means may comprise a fluid cooled mould engaging portion on said conveyor means.

Said article may be a blade, vane or component of a gas turbine engine.

The invention is illustrated, merely by way of example, in the accompanying drawings, in which:

FIG. 1 shows, partly in section, an apparatus for carrying into effect the method of the present invention, and

FIG. 2 shows, partly in section, a modification of the apparatus of FIG. I. made of Referring first to FIG. I, there is shown an apparatus for directionally casting, for example, a blade of a gas turbine engine, the apparatus being generally designated by the reference numeral 10. The apparatus 10 comprises a hollow cylindrical support member 11, on the top of which is rotatably mounted a work table 12, which is rotated in a clockwise direction, indicated by the arrow P, by means of a motor (not shown). Extending over about one third the periphery of the work table 12 is a furnace 13 of ceramic or fire brick material having an arcuate tunnel 14 therethrough. The furnace 13 may be of any known type and it will be understood that it is provided with heat seals (not shown) at the entry end 14a and the exit end 14b of the tunnel l4.

Mounted within the furnace 13 on either side of the tunnel 14 are a plurality of electric heating elements 15 which decrease in length from the entry end 14a of the tunnel to the exit end 14b. Thus these heating elements create a heat front which is disposed at an angle to the plane of the work table 12. If desired, additional heating elements (not shown) may be placed in the roof of the furnace at any suitable position. This furnace 13 for convenience may be made up of a series of modules or segments (not shown) which fit together to produce the overall furnace characteristics required. It is thus possible to replace any one segment without disturbing any other.

Mounted on the work table 12 are a plurality (14 shown in the drawing) of chills or mould stands 16, which are cooled by water or other suitable cooling fluid supplied to and extracted from the mould stands 16, by way of the hollow support member 1 l.

The operation of the apparatus 10 will be described in relation to making a single blade, although it will be understood that the apparatus is such as to continuously manufacture blades. Initially an empty mould 17 for making the blade is laced on a mould stand 16. As the work table 12 rotates through the sector A of the furnace 13, the mould 17 is heated to a temperature which is greater than the melting temperature of the change to be put therein. The rotation of the furnace may be continuous or indexed at a predetermined constant speed. A charging device 18 having a melting coil 19 is provided at the point B of the furnace and charges, through the open end 20, mould 17 with a metal change in the molten state. As the mould 17 moves to the sector C of the furnace, due to the disposition of the heat front produced by the heating elements 15, and due to the cooling effect by the mould stand I6, the charge solidifies on the mould stand 16 in an up ward direction away from the mould stand directionally solidifying the blade with an elongate columnar grain structure which is parallel to the longitudinal axis X--X of the blade. In the drawing the degree of solidification of the blade at various points within the furnace 13 is shown by cross-hatched shading. When the mould l7 emerges from the furnace 13 all the blade has the required directionally solidified structure. Thus, it will be understood that as the mould 17 moves through the furnace, the heat front progress is substantially perpendicular to the longitudinal axisX-X of the blade.

The mould 17, when it has emerged from the exit end 14b of the tunnel 14 is allowed to cool to the required temperature, and the blade is then removed therefrom.

Referring now to FIG. 2, parts of this Figure similar to corresponding parts of FIG. 1 have been designated by like reference numbers.

In this embodiment the radial location member 11 is divided into an upper chamber 31, and a lower chamber 32 by a baffle 33. The upper chamber 31 is supplied with cooling fluid, e.g.,

water, by way of a conduit 34 and the lower chamber 32 is connected to a drain conduit 35. The upper chamber 31 connects with an annular groove 36 in the radially outer surface of the member-l1 by way of a plurality of radial drillings 38. A cylindrical bearing member 37 is mounted for rotation about the member which is fixed to a rigid base 40 of the apparatus 10. The work table 12 of the apparatus is radially located from the cylindrical bearing member 37 by a plurality of spokes 41. In the embodiment of FIG. 1 the work table 12 is disc-shaped, but it will be seen that the work table in the embodiment of FIG. 2 is a ring.

Each mould stand 16 is connected, by way of passages through the work table 12, to a valve member 44 and so through flexible pipe 42 with the annular groove 36 in the member 11. Thus, cooling fluid passes from the upper chamber 31 through radial drillings 38 to the annular groove 36, from whence it flows through each of the flexible pipes 42 to the valve member 44 and thence through internal passages in the valve member 44 and work table 12 and through a nozzle 43, in the respective mould stand 16 to cool the base of the mould 17. When the cooling fluid has served its purpose, spent cooling fluid flows through the valve member 44 in the base of the mould stand, a flexible pipe 45 to an annular groove 41 in the outer surface of the member 11. From this annular groove, the spent cooling fluid passes through radial drillings 47 into the lower chamber 32, from which it passes to the drain conduit 35. The valve member 44 is manually operable by a handle 48 and normally directs the cooling fluid from the flexible pipe 42 through the work table 12 to the mould stand 16, and directs the spent cooling fluid through the flexible pipe 45 a shown. When it is desired to drain the mould stand 16, the valve member 44 is operated by handle 48 so that both flexible pipes 44, 45 are sealed off from the passage connecting the valve 44 to the mould stand 16. The construction of the valve member 44 is such that as the flexible pipes 44, 45.are sealed so the mould stand 16 is vented to atmosphere through passageways 50, one passageway admitting air to while the other drains coolingfluid from the mould stand 16.

Each mould stand 16 is surrounded by a fire brick member 51 mounted on the work table 12, each fire brick member forming a segment of an annular fire brick ring encompassing the plurality of mould stands. Thus, it will be appreciated that a single mould stand may be replaced without the necessity of disassembling the whole ring of fire brick members 51.

The work table 12 is provided with gear teeth 52 which mesh with a pinion gear 53 driven by an electric motor 54. Thus, the electric motor 54 causes rotation of the work table 12 in the direction of the arrow P. To avoid backlash or vibration of the moulds 17 during rotation of the work table 12, the latter bears on a plurality of tapered rollers 55 mounted on the base 40, the rollers taking the majority of the weight of the work table. The rollers 55 are tapered in the direction of the number 1 1.

The furnace 13 is.of similar construction to the furnace of FIG. 1 and thus will not be described in detail. However, it will be seen that the furnace in the embodiment of FIG. 2 is made up of a plurality of segments 56, for ease of maintenance. In addition the furnace 13 extends over approximately two-thirds of the periphery of the work table 12.

The furnace is lined with a radially inner ring 57 of fire brick and a radially outer ring 58 of fire brick. Both the inner ring 57 and the outer ring 58 have annular flanges 59 directed towards the moulds 17 forming with the ring of fire brick members 51 a sealing arrangement to prevent loss of heat from the tunnel 14. If so desired, additional seals (not shown), such as labyrinth seals, may be provided on the fire brick members 51 and/or on the inner ring 56 and the outer ring 58. The ring of fire brick members 51 has a trough 60 formed in its upper surface which further prevents loss of heat from the tunnel 14 which also collects debris, e.g., metal, from the moulds 17.

It will be appreciated that instead of charging the moulds with molten metal in .the furnace 13, the moulds may be chargedwith powdered or pelletized metal outside or inside the furnace. Alternatively, a rough pre-cast blade with no directional grain structure may be placed in each mould 17 outside the furnace and re-melted by the furnace 13 thus causing the blade, during its passage through the furnace 13, to be re-cast with a unidirectional grain structure.

As shown in the drawings, the furnace 13 is arcuate, but if so desired may be linear. Several furnaces, whether arcuate or linear, may be placed adjacent to each other and may use a common mechanism, such as the work table 12, for moving the moulds 17 therethrough.

In all the suggested designs mentioned above the furnace or furnaces 13 are stationary, but as an alternative it is feasible to keep the moulds stationary and move the furnace relative to them.

Dependent upon the metal being used, the atmosphere within the furnace 13 may be controlled, e.g., air, inert gas or the whole apparatus 10 may be placed in a vacuum, the heating of the furnace being suitable for the operating environmental and the metal being used.

The area below the heating elements 15 may be at any temperature as long as it is a lower temperature than the melting point of the metal. Thetemperature of the area below the heating elements 15 and the degree of heat abstraction from the mould may be controlled by the thickness of the refractory material in this area and may be supplemented by additional cooling or heating sources in this area. Alternatively, that part of the furnace below the heating elements 15 may be open to atmosphere for cooling. As a further alternative, jets of cooling fluid, e.g., air or inert gas, may be directed onto the mould 17 below the heating elements in a plane parallel to the work table 12.

The work table 12 may be made in sections for ease of replacement when renewal of the mould stands 16 is required.

Further modifications may be made to the apparatus previously described. Thus a shield may be provided between the operator and the exposed ring of fire bricks to avoid the operator being burnt by radiation. Furthermore, the entrance and exits 14a, 14b of the tunnel 14 may be sealed, for example, by a double-door arrangement, to prevent convectional air flow through the tunnel 14.

The present invention, although not so restricted, is especially useful for manufacturing turbine blades, vanes or components of a gas turbine engine. The metal used for making the blades could conveniently be any nickel or cobalt based alloy normally employed or any material particularly designed to extract optimum performance from a uni-directional structure.

The mould is heated to the required temperature at the required rate by the time it reaches the position of the melting coil 19. The time that the mould is at the required temperature, prior to receiving molten metal, may be so adjusted that the mould is fired" to develop the required properties, e.g., strength, surface finish and composition, to render the mould suitable for the directional solidification process already described. In order to develop these properties the mould, depending on chemical composition,- is preferably fired at more than l,300 C, for approximately 40 minutes. On cooling down from this temperature, changes in the structure of the mould material can take place which could impair the performance of the mould. Thus by carrying out the high temperature firing in the zone of the furnace 13 immediately prior to the melting coil 19 without subsequent cooling therebetween, it is possible to avoid reducing these changes until after the metal has solidified.

To achieve a greater output from the apparatus 10 a plurality of blades could be produced in a single mould. Thus, each mould would merely be shaped to produce the required number of blades with suitable channelling to ensure that the molten metal would be supplied to all parts of the mould.

It will be appreciated that the whole apparatus 10 may be automated. This suitable mechanisms may feed empty moulds 17 into the furnace l3, and remove the article from the mould when it leaves the furnace.

We claim:

l. A method of producing a metal article having a unidirectional grain structure in a given direction, comprising the steps of heating a mould for the article to a temperature above the melting point of molten metal in the mould, efiecting relative movement between the mould and a furnace in a horizontal direction so that said mould moves through the furnace, said furnace having a heat front which is disposed at an oblique angle with respect to the direction of relative movement in a horizontal direction between the mould and the furnace, so that said heat from moves in a vertical direction with respect to said mould substantially perpendicular to said direction towards one end of the mould, and cooling the opposite end of said mould so that said heat front produces said grain structure in the article.

2. In a method of producing a metal article having a unidirectional grain structure in a given direction comprising the steps of a. heating a mould for the article to a temperature above the melting point of molten metal in the mould,

b. effecting relative movement between the mould and a furnace so that said mould moves through the furnace, said furnace having a heat front which is disposed with respect to the direction of relative movement between the mould and the furnace, so that said heat front moves nearly perpendicular to said direction towards one end of the mould,

c. cooling the opposite end of said rnould so that said heat front produces said grain structure in the article,

d. removing the mould containing the metal article thus produced from the cooling area, the improvement comprising:

i. disposing said heat front at an oblique angle with respect to the direction of relative movement between the furnace and the mould,

ii. effecting relative movement between the mould and the furnace in a substantially horizontal direction causing vertical movement of the heat front along the axis of the mould from one end of the mould to the other.

3. A method as claimed in claim 1 in which said cooling is efiected by contacting said opposite end of said mould with a cooled surface.

4. A method as claimed in claim 1 in which said cooling is effected by directing a cooling medium upon said opposite end of the mould.

5. A method as claimed in claim 1 in which said article is a blade, vane or component of a gas turbine engine.

6. A method as claimed in l in which said metal is an alloy.

7. A method as claimed in claim 1 in which said mould is charged with molten metal while in the furnace.

8. A method as claimed in claim 1 in which said metal is a powder or pellets and is placed in said mould prior to melting.

9. A method as claimed in claim 1 in which said furnace is stationary and said mould is moved therethrough.

10. A method as claimed in claim 2 wherein steps (a) through (d) are repeated, in series, thereby providing a continuous method of producing said metal article having unidirectional grain structure in a given direction.

I i i 

1. A method of producing a metal article having a unidirectional grain structure in a given direction, comprising the steps of heating a mould for the article to a temperature above the melting point of molten metal in the mould, effecting relative movement between the mould and a furnace in a horizontal direction so that said mould moves through the furnace, said furnace having a heat front which is disposed at an oblique angle with respect to the direction of relative movement in a horizontal direction between the mould and the furnace, so that said heat front moves in a vertical direction with respect to said mould substantially perpendicular to said direction towards one end of the mould, and cooling the opposite end of said mould so that said heat front produces said grain structure in the article.
 2. In a method of producing a metal article having a unidirectional grain structure in a given direction comprising the steps of a. heating a mould for the article to a temperature above the melting point of molten metal in the mould, b. effecting relative movement between the mould and a furnace so that said mould moves through the furnace, said furnace having a heat front which is disposed with respect to the direction of relative movement between the mould and the furnace, so that said heat front moves nearly perpendicular to said direction towards one end of the mould, c. cooling the opposite end of said mould so that said heat front produces said grain structure in the article, d. removing the mould containing the metal article thus produced from the cooling area, the improvement comprising: i. disposing said heat front at an oblique angle with respect to the direction of relative movement between the furnace and the mould, ii. effecting relative movement between the mould and the furnace in a substantially horizontal direction causing vertical movement of the heat front along the axis of the mould from one end oF the mould to the other.
 3. A method as claimed in claim 1 in which said cooling is effected by contacting said opposite end of said mould with a cooled surface.
 4. A method as claimed in claim 1 in which said cooling is effected by directing a cooling medium upon said opposite end of the mould.
 5. A method as claimed in claim 1 in which said article is a blade, vane or component of a gas turbine engine.
 6. A method as claimed in 1 in which said metal is an alloy.
 7. A method as claimed in claim 1 in which said mould is charged with molten metal while in the furnace.
 8. A method as claimed in claim 1 in which said metal is a powder or pellets and is placed in said mould prior to melting.
 9. A method as claimed in claim 1 in which said furnace is stationary and said mould is moved therethrough.
 10. A method as claimed in claim 2 wherein steps (a) through (d) are repeated, in series, thereby providing a continuous method of producing said metal article having unidirectional grain structure in a given direction. 